Duplex printing is a process in which one or more images are applied by a printing system to both a first surface and a second surface of a substrate. During some duplex printing processes, ink printed onto a substrate offsets from the substrate to various parts of printing systems such as, but not limited to, rollers, belts, baffles, winders, unwinders, stackers, etc.
Some methods for duplex printing involve first printing one or more images onto one of the first surface and the second surface of a substrate during a first printing process using a printing system, then printing one or more other images on the other of the first surface and the second surface by way of a second printing process using the same or different printing system.
For example, if the duplex printing is conducted by one or more printing systems configured for simplex printing (i.e. printing one or more images on only one of the first surface and second surface), the substrate is commonly inverted and run through the same or different print system to apply one or more other images to the other of the first surface and the second surface of the substrate.
Various conventional printing systems configured for simplex printing prevent offset of the image during the above discussed first printing process by optimizing a number of different options that include controlling: 1) ink/substrate and/or drum/roller surface temperature, 2) drum/roller surface finish, 3) absence of relative motion between ink/substrate and drum/roller surfaces, and 4) application of a release agent during the first printing process.
Conventional printing systems, however, particularly if they are set up for only simplex printing, ignore applying release agent, for example, to the other of the first surface and the second surface because that surface is typically blank (or has a pre-printed image that simply will not offset).
However, when a substrate having been subjected to the first printing process is inverted and run through a print system configured for simplex printing for the second printing process, ink applied to the substrate during the first printing process will offset to various parts of the printing system. This is because, as discussed above, a conventional simplex configured printing system does not normally have offset issues relating to a substrate that has an image applied to a backside surface of the substrate.
Though some release agent applied during the first printing process may remain on the surface having the image applied during the first printing process, this release agent is often absorbed by the substrate or migrates to various portions of the substrate between the first printing process and the second printing process. As such, there is not enough release agent present on the surface of the substrate, or at least in the desired position on the surface of the substrate, to prevent ink offset of the image applied by the first printing process during the second printing process to various portions of the print system.